Tracking reference signal configuration design

ABSTRACT

A method, an apparatus, and a computer program product for wireless communication are provided. The apparatus may determine a signal configuration for transmitting a tracking reference signal (TRS) to a user equipment (UE). The signal configuration may identify a subset of locations, of a set of locations included in a transmission window, that is to be used to transmit the TRS, and the signal configuration may be selected to assist the UE with one or more measurements. The apparatus may transmit, based at least in part on the signal configuration, the TRS in the subset of locations. Numerous other aspects are provided.

CROSS REFERENCE TO RELATED APPLICATION UNDER 35 U.S.C. § 119

This application claims priority to U.S. Provisional Patent ApplicationNo. 62/459,320 filed on Feb. 15, 2017 entitled “TRACKING REFERENCESIGNAL CONFIGURATION DESIGN,” which is incorporated by reference herein.

BACKGROUND Field

Aspects of the present disclosure generally relate to wirelesscommunication, and more particularly to techniques and apparatuses fortracking reference signal configuration design.

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power, and/or the like). Examples of such multiple-accesstechnologies include code division multiple access (CDMA) systems, timedivision multiple access (TDMA) systems, frequency-division multipleaccess (FDMA) systems, orthogonal frequency-division multiple access(OFDMA) systems, single-carrier frequency-division multiple access(SC-FDMA) systems, time division synchronous code division multipleaccess (TD-SCDMA) systems, and Long Term Evolution (LTE).LTE/LTE-Advanced is a set of enhancements to the Universal MobileTelecommunications System (UMTS) mobile standard promulgated by theThird Generation Partnership Project (3GPP).

A wireless communication network may include a number of base stations(BSs) that can support communication for a number of user equipment(UEs). A UE may communicate with a BS via the downlink and uplink. Thedownlink (or forward link) refers to the communication link from the BSto the UE, and the uplink (or reverse link) refers to the communicationlink from the UE to the BS. As will be described in more detail herein,a BS may be referred to as a Node B, a gNB, an access point (AP), aradio head, a transmit receive point (TRP), a new radio (NR) BS, a 5GNode B, and/or the like.

The above multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless communication devices to communicate on a municipal,national, regional, and even global level. New radio (NR), which mayalso be referred to as 5G, is a set of enhancements to the LTE mobilestandard promulgated by the Third Generation Partnership Project (3GPP).NR is designed to better support mobile broadband Internet access byimproving spectral efficiency, lowering costs, improving services,making use of new spectrum, and better integrating with other openstandards using OFDM with a cyclic prefix (CP) (CP-OFDM) on the downlink(DL), using CP-OFDM and/or SC-FDM (e.g., also known as discrete Fouriertransform spread ODFM (DFT-s-OFDM)) on the uplink (UL), as well assupporting beamforming, multiple-input multiple-output (MIMO) antennatechnology, and carrier aggregation. However, as the demand for mobilebroadband access continues to increase, there exists a need for furtherimprovements in LTE and NR technologies. Preferably, these improvementsshould be applicable to other multiple access technologies and thetelecommunication standards that employ these technologies.

SUMMARY

In an aspect of the disclosure, a method, an apparatus, and a computerprogram product are provided.

In some aspects, the method may include determining, by a base station,a signal configuration for transmitting a tracking reference signal(TRS) to a user equipment (UE), where the signal configuration mayidentify a subset of locations, of a set of locations included in atransmission window, that is to be used to transmit the TRS, and thesignal configuration selected to assist the UE with one or moremeasurements; and transmitting, by the base station and based at leastin part on the signal configuration, the TRS in the subset of locations.

In some aspects, the apparatus may include a memory and at least oneprocessor coupled to the memory. The at least one processor may beconfigured to determine a signal configuration for transmitting a TRS toa UE, where the signal configuration may identify a subset of locations,of a set of locations included in a transmission window, that is to beused to transmit the TRS, and the signal configuration selected toassist the UE with one or more measurements; and transmit, based atleast in part on the signal configuration, the TRS in the subset oflocations.

In some aspects, the apparatus may include means for determining asignal configuration for transmitting a TRS to a UE, where the signalconfiguration may identify a subset of locations, of a set of locationsincluded in a transmission window, that is to be used to transmit theTRS, and the signal configuration selected to assist the UE with one ormore measurements; and means for transmitting, based at least in part onthe signal configuration, the TRS in the subset of locations.

In some aspects, the computer program product may include anon-transitory computer-readable medium storing computer executablecode. The code may include code for determining a signal configurationfor transmitting a TRS to a UE, where the signal configuration mayidentify a subset of locations, of a set of locations included in atransmission window, that is to be used to transmit the TRS, and thesignal configuration selected to assist the UE with one or moremeasurements; and transmitting, based at least in part on the signalconfiguration, the TRS in the subset of locations.

In some aspects, the method may include transmitting, by a UE and to abase station, signal information for determining a signal configurationassociated with a TRS; and receiving, by the UE, the TRS based at leastin part on transmitting the signal information to the base station,wherein the TRS is received in a subset of locations, of a pluralitylocations included in a transmission window.

In some aspects, the apparatus may include a memory and at least oneprocessor coupled to the memory. The at least one processor may beconfigured to transmit, to a base station, signal information fordetermining a signal configuration associated with a TRS; and receivethe TRS based at least in part on transmitting the signal information tothe base station, wherein the TRS is received in a subset of locations,of a plurality locations included in a transmission window.

In some aspects, the apparatus may include means for transmitting, to abase station, signal information for determining a signal configurationassociated with a TRS; and means for receiving the TRS based at least inpart on transmitting the signal information to the base station, whereinthe TRS is received in a subset of locations, of a plurality locationsincluded in a transmission window.

In some aspects, the computer program product may include anon-transitory computer-readable medium storing computer executablecode. The code may include code for transmitting, to a base station,signal information for determining a signal configuration associatedwith a TRS; and receiving the TRS based at least in part on transmittingthe signal information to the base station, wherein the TRS is receivedin a subset of locations, of a plurality locations included in atransmission window.

Aspects generally include a method, apparatus, system, computer programproduct, non-transitory computer-readable medium, user equipment, basestation, wireless communication device, and processing system assubstantially described herein with reference to and as illustrated bythe accompanying drawings and specification.

The foregoing has outlined rather broadly the features and technicaladvantages of examples according to the disclosure in order that thedetailed description that follows may be better understood. Additionalfeatures and advantages will be described hereinafter. The conceptionand specific examples disclosed may be readily utilized as a basis formodifying or designing other structures for carrying out the samepurposes of the present disclosure. Such equivalent constructions do notdepart from the scope of the appended claims. Characteristics of theconcepts disclosed herein, both their organization and method ofoperation, together with associated advantages will be better understoodfrom the following description when considered in connection with theaccompanying figures. Each of the figures is provided for the purpose ofillustration and description, and not as a definition of the limits ofthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is diagram illustrating an example of a wireless communicationnetwork.

FIG. 2 is a diagram illustrating an example of a base station incommunication with a user equipment (UE) in a wireless communicationnetwork.

FIG. 3 is a diagram illustrating an example of a frame structure in awireless communication network.

FIG. 4 is a diagram illustrating two example subframe formats with thenormal cyclic prefix.

FIG. 5 is a diagram illustrating an example logical architecture of adistributed radio access network (RAN).

FIG. 6 is a diagram illustrating an example physical architecture of adistributed RAN.

FIG. 7 is a diagram illustrating an example of a downlink (DL)-centricwireless communication structure.

FIG. 8 is a diagram illustrating an example of an uplink (UL)-centricwireless communication structure.

FIG. 9 is a diagram illustrating an example of determining a signalconfiguration for a transmitting a tracking reference signal (TRS) to auser equipment, and transmitting the TRS based at least in part on thesignal configuration.

FIG. 10 is a flow chart of a method of wireless communication.

FIG. 11 is a conceptual data flow diagram illustrating the data flowbetween different modules/means/components in an example apparatus.

FIG. 12 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purposes of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well-known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawings by various blocks, modules, components,circuits, steps, processes, algorithms, and/or the like (collectivelyreferred to as “elements”). These elements may be implemented usingelectronic hardware, computer software, or any combination thereof.Whether such elements are implemented as hardware or software dependsupon the particular application and design constraints imposed on theoverall system.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions,and/or the like, whether referred to as software, firmware, middleware,microcode, hardware description language, or otherwise.

Accordingly, in one or more example embodiments, the functions describedmay be implemented in hardware, software, firmware, or any combinationthereof. If implemented in software, the functions may be stored on orencoded as one or more instructions or code on a computer-readablemedium. Computer-readable media includes computer storage media. Storagemedia may be any available media that can be accessed by a computer. Byway of example, and not limitation, such computer-readable media cancomprise a random-access memory (RAM), a read-only memory (ROM), anelectrically erasable programmable ROM (EEPROM), compact disk ROM(CD-ROM) or other optical disk storage, magnetic disk storage or othermagnetic storage devices, combinations of the aforementioned types ofcomputer-readable media, or any other medium that can be used to storecomputer executable code in the form of instructions or data structuresthat can be accessed by a computer.

An access point (“AP”) may comprise, be implemented as, or known as aNodeB, a Radio Network Controller (“RNC”), an eNodeB (eNB), a BaseStation Controller (“BSC”), a Base Transceiver Station (“BTS”), a BaseStation (“BS”), a Transceiver Function (“TF”), a Radio Router, a RadioTransceiver, a Basic Service Set (“BSS”), an Extended Service Set(“ESS”), a Radio Base Station (“RBS”), a Node B (NB), a gNB, a 5G NB, aNR BS, a Transmit Receive Point (TRP), or some other terminology.

An access terminal (“AT”) may comprise, be implemented as, or be knownas an access terminal, a subscriber station, a subscriber unit, a mobilestation, a remote station, a remote terminal, a user terminal, a useragent, a user device, user equipment (UE), a user station, a wirelessnode, or some other terminology. In some aspects, an access terminal maycomprise a cellular telephone, a smart phone, a cordless telephone, aSession Initiation Protocol (“SIP”) phone, a wireless local loop (“WLL”)station, a personal digital assistant (“PDA”), a tablet, a netbook, asmartbook, an ultrabook, a handheld device having wireless connectioncapability, a Station (“STA”), or some other suitable processing deviceconnected to a wireless modem. Accordingly, one or more aspects taughtherein may be incorporated into a phone (e.g., a cellular phone, a smartphone), a computer (e.g., a desktop), a portable communication device, aportable computing device (e.g., a laptop, a personal data assistant, atablet, a netbook, a smartbook, an ultrabook), wearable device (e.g.,smart watch, smart glasses, smart bracelet, smart wristband, smart ring,smart clothing, and/or the like), medical devices or equipment,biometric sensors/devices, an entertainment device (e.g., music device,video device, satellite radio, gaming device, and/or the like), avehicular component or sensor, smart meters/sensors, industrialmanufacturing equipment, a global positioning system device, or anyother suitable device that is configured to communicate via a wirelessor wired medium. In some aspects, the node is a wireless node. Awireless node may provide, for example, connectivity for or to a network(e.g., a wide area network such as the Internet or a cellular network)via a wired or wireless communication link. Some UEs may be consideredmachine-type communication (MTC) UEs, which may include remote devicesthat may communicate with a base station, another remote device, or someother entity. Machine type communications (MTC) may refer tocommunication involving at least one remote device on at least one endof the communication and may include forms of data communication whichinvolve one or more entities that do not necessarily need humaninteraction. MTC UEs may include UEs that are capable of MTCcommunications with MTC servers and/or other MTC devices through PublicLand Mobile Networks (PLMN), for example. Examples of MTC devicesinclude sensors, meters, location tags, monitors, drones, robots/roboticdevices, and/or the like. MTC UEs, as well as other types of UEs, may beimplemented as NB-IoT (narrowband internet of things) devices.

It is noted that while aspects may be described herein using terminologycommonly associated with 3G and/or 4G wireless technologies, aspects ofthe present disclosure can be applied in other generation-basedcommunication systems, such as 5G and later, including NR technologies.

FIG. 1 is a diagram illustrating a network 100 in which aspects of thepresent disclosure may be practiced. The network 100 may be an LTEnetwork or some other wireless network, such as a 5G or NR network.Wireless network 100 may include a number of BSs 110 (shown as BS 110 a,BS 110 b, BS 110 c, and BS 110 d) and other network entities. A BS is anentity that communicates with user equipment (UEs) and may also bereferred to as a base station, a NR BS, a Node B, a gNB, a 5G NB, anaccess point, a TRP, and/or the like. Each BS may provide communicationcoverage for a particular geographic area. In 3GPP, the term “cell” canrefer to a coverage area of a BS and/or a BS subsystem serving thiscoverage area, depending on the context in which the term is used.

A BS may provide communication coverage for a macro cell, a pico cell, afemto cell, and/or another type of cell. A macro cell may cover arelatively large geographic area (e.g., several kilometers in radius)and may allow unrestricted access by UEs with service subscription. Apico cell may cover a relatively small geographic area and may allowunrestricted access by UEs with service subscription. A femto cell maycover a relatively small geographic area (e.g., a home) and may allowrestricted access by UEs having association with the femto cell (e.g.,UEs in a closed subscriber group (CSG)). A BS for a macro cell may bereferred to as a macro BS. A BS for a pico cell may be referred to as apico BS. A BS for a femto cell may be referred to as a femto BS or ahome BS. In the example shown in FIG. 1, a BS 110 a may be a macro BSfor a macro cell 102 a, a BS 110 b may be a pico BS for a pico cell 102b, and a BS 110 c may be a femto BS for a femto cell 102 c. A BS maysupport one or multiple (e.g., three) cells. The terms “eNB”, “basestation”, “NR BS”, “gNB”, “TRP”, “AP”, “node B”, “5G NB”, and “cell” maybe used interchangeably herein.

In some examples, a cell may not necessarily be stationary, and thegeographic area of the cell may move according to the location of amobile BS. In some examples, the BSs may be interconnected to oneanother and/or to one or more other BSs or network nodes (not shown) inthe access network 100 through various types of backhaul interfaces suchas a direct physical connection, a virtual network, and/or the likeusing any suitable transport network.

Wireless network 100 may also include relay stations. A relay station isan entity that can receive a transmission of data from an upstreamstation (e.g., a BS or a UE) and send a transmission of the data to adownstream station (e.g., a UE or a BS). A relay station may also be aUE that can relay transmissions for other UEs. In the example shown inFIG. 1, a relay station 110 d may communicate with macro BS 110 a and aUE 120 d in order to facilitate communication between BS 110 a and UE120 d. A relay station may also be referred to as a relay BS, a relaybase station, a relay, and/or the like.

Wireless network 100 may be a heterogeneous network that includes BSs ofdifferent types, e.g., macro BSs, pico BSs, femto BSs, relay BSs, and/orthe like. These different types of BSs may have different transmit powerlevels, different coverage areas, and different impact on interferencein wireless network 100. For example, macro BSs may have a high transmitpower level (e.g., 5 to 40 Watts) whereas pico BSs, femto BSs, and relayBSs may have lower transmit power levels (e.g., 0.1 to 2 Watts).

A network controller 130 may couple to a set of BSs and may providecoordination and control for these BSs. Network controller 130 maycommunicate with the BSs via a backhaul. The BSs may also communicatewith one another, e.g., directly or indirectly via a wireless orwireline backhaul.

UEs 120 (e.g., 120 a, 120 b, 120 c) may be dispersed throughout wirelessnetwork 100, and each UE may be stationary or mobile. A UE may also bereferred to as an access terminal, a terminal, a mobile station, asubscriber unit, a station, and/or the like. A UE may be a cellularphone (e.g., a smart phone), a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, alaptop computer, a cordless phone, a wireless local loop (WLL) station,a tablet, a camera, a gaming device, a netbook, a smartbook, anultrabook, medical device or equipment, biometric sensors/devices,wearable devices (smart watches, smart clothing, smart glasses, smartwrist bands, smart jewelry (e.g., smart ring, smart bracelet)), anentertainment device (e.g., a music or video device, or a satelliteradio), a vehicular component or sensor, smart meters/sensors,industrial manufacturing equipment, a global positioning system device,or any other suitable device that is configured to communicate via awireless or wired medium. Some UEs may be considered evolved or enhancedmachine-type communication (eMTC) UEs. MTC and eMTC UEs include, forexample, robots, drones, remote devices, such as sensors, meters,monitors, location tags, and/or the like, that may communicate with abase station, another device (e.g., remote device), or some otherentity. A wireless node may provide, for example, connectivity for or toa network (e.g., a wide area network such as Internet or a cellularnetwork) via a wired or wireless communication link. Some UEs may beconsidered Internet-of-Things (IoT) devices. Some UEs may be considereda Customer Premises Equipment (CPE).

In FIG. 1, a solid line with double arrows indicates desiredtransmissions between a UE and a serving BS, which is a BS designated toserve the UE on the downlink and/or uplink. A dashed line with doublearrows indicates potentially interfering transmissions between a UE anda BS.

In general, any number of wireless networks may be deployed in a givengeographic area. Each wireless network may support a particular RAT andmay operate on one or more frequencies. A RAT may also be referred to asa radio technology, an air interface, and/or the like. A frequency mayalso be referred to as a carrier, a frequency channel, and/or the like.Each frequency may support a single RAT in a given geographic area inorder to avoid interference between wireless networks of different RATs.In some cases, NR or 5G RAT networks may be deployed.

In some examples, access to the air interface may be scheduled, whereina scheduling entity (e.g., a base station) allocates resources forcommunication among some or all devices and equipment within thescheduling entity's service area or cell. Within the present disclosure,as discussed further below, the scheduling entity may be responsible forscheduling, assigning, reconfiguring, and releasing resources for one ormore subordinate entities. That is, for scheduled communication,subordinate entities utilize resources allocated by the schedulingentity.

Base stations are not the only entities that may function as ascheduling entity. That is, in some examples, a UE may function as ascheduling entity, scheduling resources for one or more subordinateentities (e.g., one or more other UEs). In this example, the UE isfunctioning as a scheduling entity, and other UEs utilize resourcesscheduled by the UE for wireless communication. A UE may function as ascheduling entity in a peer-to-peer (P2P) network, and/or in a meshnetwork. In a mesh network example, UEs may optionally communicatedirectly with one another in addition to communicating with thescheduling entity.

Thus, in a wireless communication network with a scheduled access totime-frequency resources and having a cellular configuration, a P2Pconfiguration, and a mesh configuration, a scheduling entity and one ormore subordinate entities may communicate utilizing the scheduledresources.

As indicated above, FIG. 1 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 1.

FIG. 2 shows a block diagram 200 of a design of base station 110 and UE120, which may be one of the base stations and one of the UEs in FIG. 1.Base station 110 may be equipped with T antennas 234 a through 234 t,and UE 120 may be equipped with R antennas 252 a through 252 r, where ingeneral T≥1 and R≥1.

At base station 110, a transmit processor 220 may receive data from adata source 212 for one or more UEs, select one or more modulation andcoding schemes (MCS) for each UE based at least in part on channelquality indicators (CQIs) received from the UE, process (e.g., encodeand modulate) the data for each UE based at least in part on the MCS(s)selected for the UE, and provide data symbols for all UEs. Transmitprocessor 220 may also process system information (e.g., for semi-staticresource partitioning information (SRPI), and/or the like) and controlinformation (e.g., CQI requests, grants, upper layer signaling, and/orthe like) and provide overhead symbols and control symbols. Transmitprocessor 220 may also generate reference symbols for reference signals(e.g., the CRS) and synchronization signals (e.g., the primarysynchronization signal (PSS) and secondary synchronization signal(SSS)). A transmit (TX) multiple-input multiple-output (MIMO) processor230 may perform spatial processing (e.g., precoding) on the datasymbols, the control symbols, the overhead symbols, and/or the referencesymbols, if applicable, and may provide T output symbol streams to Tmodulators (MODs) 232 a through 232 t. Each modulator 232 may process arespective output symbol stream (e.g., for OFDM and/or the like) toobtain an output sample stream. Each modulator 232 may further process(e.g., convert to analog, amplify, filter, and upconvert) the outputsample stream to obtain a downlink signal. T downlink signals frommodulators 232 a through 232 t may be transmitted via T antennas 234 athrough 234 t, respectively. According to certain aspects described inmore detail below, the synchronization signals can be generated withlocation encoding to convey additional information.

At UE 120, antennas 252 a through 252 r may receive the downlink signalsfrom base station 110 and/or other base stations and may providereceived signals to demodulators (DEMODs) 254 a through 254 r,respectively. Each demodulator 254 may condition (e.g., filter, amplify,downconvert, and digitize) a received signal to obtain input samples.Each demodulator 254 may further process the input samples (e.g., forOFDM and/or the like) to obtain received symbols. A MIMO detector 256may obtain received symbols from all R demodulators 254 a through 254 r,perform MIMO detection on the received symbols if applicable, andprovide detected symbols. A receive (RX) processor 258 may process(e.g., demodulate and decode) the detected symbols, provide decoded datafor UE 120 to a data sink 260, and provide decoded control informationand system information to a controller/processor 280. A channelprocessor may determine RSRP, RSSI, RSRQ, CQI, and/or the like.

On the uplink, at UE 120, a transmit processor 264 may receive andprocess data from a data source 262 and control information (e.g., forreports comprising RSRP, RSSI, RSRQ, CQI, and/or the like) fromcontroller/processor 280. Transmit processor 264 may also generatereference symbols for one or more reference signals. The symbols fromtransmit processor 264 may be precoded by a TX MIMO processor 266 ifapplicable, further processed by modulators 254 a through 254 r (e.g.,for DFT-s-OFDM, CP-OFDM, and/or the like), and transmitted to basestation 110. At base station 110, the uplink signals from UE 120 andother UEs may be received by antennas 234, processed by demodulators232, detected by a MIMO detector 236 if applicable, and furtherprocessed by a receive processor 238 to obtain decoded data and controlinformation sent by UE 120. Receive processor 238 may provide thedecoded data to a data sink 239 and the decoded control information tocontroller/processor 240. Base station 110 may include communicationunit 244 and communicate to network controller 130 via communicationunit 244. Network controller 130 may include communication unit 294,controller/processor 290, and memory 292.

Controllers/processors 240 and 280 and/or any other component(s) in FIG.2 may direct the operation at base station 110 and UE 120, respectively,to perform tracking reference signal configuration. For example,controller/processor 280 and/or other processors and modules at basestation 110, may perform or direct operations of UE 120 to performtracking reference signal configuration design. For example,controller/processor 280 and/or other controllers/processors and modulesat BS 110 may perform or direct operations of, for example, method 1000of FIG. 10 and/or other processes as described herein. In some aspects,one or more of the components shown in FIG. 2 may be employed to performexample method 1000 of FIG. 10 and/or other processes for the techniquesdescribed herein. Memories 242 and 282 may store data and program codesfor BS 110 and UE 120, respectively. A scheduler 246 may schedule UEsfor data transmission on the downlink and/or uplink.

As indicated above, FIG. 2 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 2.

FIG. 3 shows an example frame structure 300 for FDD in atelecommunications system (e.g., LTE). The transmission timeline foreach of the downlink and uplink may be partitioned into units of radioframes. Each radio frame may have a predetermined duration (e.g., 10milliseconds (ms)) and may be partitioned into 10 subframes with indicesof 0 through 9. Each subframe may include two slots. Each radio framemay thus include 20 slots with indices of 0 through 19. Each slot mayinclude L symbol periods, e.g., seven symbol periods for a normal cyclicprefix (as shown in FIG. 3) or six symbol periods for an extended cyclicprefix. The 2L symbol periods in each subframe may be assigned indicesof 0 through 2L−1.

While some techniques are described herein in connection with frames,subframes, slots, and/or the like, these techniques may equally apply toother types of wireless communication structures, which may be referredto using terms other than “frame,” “subframe,” “slot,” and/or the likein 5G NR. In some aspects, a wireless communication structure may referto a periodic time-bounded communication unit defined by a wirelesscommunication standard and/or protocol.

In certain telecommunications (e.g., LTE), a BS may transmit a primarysynchronization signal (PSS) and a secondary synchronization signal(SSS) on the downlink in the center of the system bandwidth for eachcell supported by the BS. The PSS and SSS may be transmitted in symbolperiods 6 and 5, respectively, in subframes 0 and 5 of each radio framewith the normal cyclic prefix, as shown in FIG. 3. The PSS and SSS maybe used by UEs for cell search and acquisition. The BS may transmit acell-specific reference signal (CRS) across the system bandwidth foreach cell supported by the BS. The CRS may be transmitted in certainsymbol periods of each subframe and may be used by the UEs to performchannel estimation, channel quality measurement, and/or other functions.The BS may also transmit a physical broadcast channel (PBCH) in symbolperiods 0 to 3 in slot 1 of certain radio frames. The PBCH may carrysome system information. The BS may transmit other system informationsuch as system information blocks (SIBs) on a physical downlink sharedchannel (PDSCH) in certain subframes. The BS may transmit controlinformation/data on a physical downlink control channel (PDCCH) in thefirst B symbol periods of a subframe, where B may be configurable foreach subframe. The BS may transmit traffic data and/or other data on thePDSCH in the remaining symbol periods of each subframe.

In other systems (e.g., such NR or 5G systems), a Node B may transmitthese or other signals in these locations or in different locations ofthe subframe.

As indicated above, FIG. 3 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 3.

FIG. 4 shows two example subframe formats 410 and 420 with the normalcyclic prefix. The available time frequency resources may be partitionedinto resource blocks. Each resource block may cover 12 subcarriers inone slot and may include a number of resource elements. Each resourceelement may cover one subcarrier in one symbol period and may be used tosend one modulation symbol, which may be a real or complex value.

Subframe format 410 may be used for two antennas. A CRS may betransmitted from antennas 0 and 1 in symbol periods 0, 4, 7 and 11. Areference signal is a signal that is known a priori by a transmitter anda receiver and may also be referred to as pilot. A CRS is a referencesignal that is specific for a cell, e.g., generated based at least inpart on a cell identity (ID). In FIG. 4, for a given resource elementwith label Ra, a modulation symbol may be transmitted on that resourceelement from antenna a, and no modulation symbols may be transmitted onthat resource element from other antennas. Subframe format 420 may beused with four antennas. A CRS may be transmitted from antennas 0 and 1in symbol periods 0, 4, 7 and 11 and from antennas 2 and 3 in symbolperiods 1 and 8. For both subframe formats 410 and 420, a CRS may betransmitted on evenly spaced subcarriers, which may be determined basedat least in part on cell ID. CRSs may be transmitted on the same ordifferent subcarriers, depending on their cell IDs. For both subframeformats 410 and 420, resource elements not used for the CRS may be usedto transmit data (e.g., traffic data, control data, and/or other data).

The PSS, SSS, CRS and PBCH in LTE are described in 3GPP TS 36.211,entitled “Evolved Universal Terrestrial Radio Access (E-UTRA); PhysicalChannels and Modulation,” which is publicly available.

An interlace structure may be used for each of the downlink and uplinkfor FDD in certain telecommunications systems (e.g., LTE). For example,Q interlaces with indices of 0 through Q−1 may be defined, where Q maybe equal to 4, 6, 8, 10, or some other value. Each interlace may includesubframes that are spaced apart by Q frames. In particular, interlace qmay include subframes q, q+Q, q+2Q, and/or the like, where q∈{0, . . . ,Q−1}.

The wireless network may support hybrid automatic retransmission request(HARQ) for data transmission on the downlink and uplink. For HARQ, atransmitter (e.g., a BS) may send one or more transmissions of a packetuntil the packet is decoded correctly by a receiver (e.g., a UE) or someother termination condition is encountered. For synchronous HARQ, alltransmissions of the packet may be sent in subframes of a singleinterlace. For asynchronous HARQ, each transmission of the packet may besent in any subframe.

A UE may be located within the coverage of multiple BSs. One of theseBSs may be selected to serve the UE. The serving BS may be selectedbased at least in part on various criteria such as received signalstrength, received signal quality, path loss, and/or the like. Receivedsignal quality may be quantified by a signal-to-noise-and-interferenceratio (SINR), or a reference signal received quality (RSRQ), or someother metric. The UE may operate in a dominant interference scenario inwhich the UE may observe high interference from one or more interferingBSs.

While aspects of the examples described herein may be associated withLTE technologies, aspects of the present disclosure may be applicablewith other wireless communication systems, such as NR or 5Gtechnologies.

New radio (NR) may refer to radios configured to operate according to anew air interface (e.g., other than Orthogonal Frequency DivisionalMultiple Access (OFDMA)-based air interfaces) or fixed transport layer(e.g., other than Internet Protocol (IP)). In aspects, NR may utilizeOFDM with a CP (herein referred to as cyclic prefix OFDM or CP-OFDM)and/or SC-FDM on the uplink, may utilize CP-OFDM on the downlink andinclude support for half-duplex operation using TDD. In aspects, NR may,for example, utilize OFDM with a CP (herein referred to as CP-OFDM)and/or discrete Fourier transform spread orthogonal frequency-divisionmultiplexing (DFT-s-OFDM) on the uplink, may utilize CP-OFDM on thedownlink and include support for half-duplex operation using TDD. NR mayinclude Enhanced Mobile Broadband (eMBB) service targeting widebandwidth (e.g., 80 megahertz (MHz) and beyond), millimeter wave (mmW)targeting high carrier frequency (e.g., 60 gigahertz (GHz)), massive MTC(mMTC) targeting non-backward compatible MTC techniques, and/or missioncritical targeting ultra reliable low latency communications (URLLC)service.

A single component carrier bandwidth of 100 MHZ may be supported. NRresource blocks may span 12 sub-carriers with a sub-carrier bandwidth of75 kilohertz (kHz) over a 0.1 ms duration. Each radio frame may include50 subframes with a length of 10 ms. Consequently, each subframe mayhave a length of 0.2 ms. Each subframe may indicate a link direction(e.g., DL or UL) for data transmission and the link direction for eachsubframe may be dynamically switched. Each subframe may include DL/ULdata as well as DL/UL control data. UL and DL subframes for NR may be asdescribed in more detail below with respect to FIGS. 7 and 8.

Beamforming may be supported and beam direction may be dynamicallyconfigured. MIMO transmissions with precoding may also be supported.MIMO configurations in the DL may support up to 8 transmit antennas withmulti-layer DL transmissions up to 8 streams and up to 2 streams per UE.Multi-layer transmissions with up to 2 streams per UE may be supported.Aggregation of multiple cells may be supported with up to 8 servingcells. Alternatively, NR may support a different air interface, otherthan an OFDM-based interface. NR networks may include entities suchcentral units or distributed units.

The RAN may include a central unit (CU) and distributed units (DUs). ANR BS (e.g., gNB, 5G Node B, Node B, transmit receive point (TRP),access point (AP)) may correspond to one or multiple BSs. NR cells canbe configured as access cells (ACells) or data only cells (DCells). Forexample, the RAN (e.g., a central unit or distributed unit) canconfigure the cells. DCells may be cells used for carrier aggregation ordual connectivity, but not used for initial access, cellselection/reselection, or handover. In some cases, DCells may nottransmit synchronization signals—in some cases DCells may transmit SS.NR BSs may transmit downlink signals to UEs indicating the cell type.Based at least in part on the cell type indication, the UE maycommunicate with the NR BS. For example, the UE may determine NR BSs toconsider for cell selection, access, handover, and/or measurement basedat least in part on the indicated cell type.

As indicated above, FIG. 4 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 4.

FIG. 5 illustrates an example logical architecture of a distributed RAN500, according to aspects of the present disclosure. A 5G access node506 may include an access node controller (ANC) 502. The ANC may be acentral unit (CU) of the distributed RAN 500. The backhaul interface tothe next generation core network (NG-CN) 504 may terminate at the ANC.The backhaul interface to neighboring next generation access nodes(NG-ANs) may terminate at the ANC. The ANC may include one or more TRPs508 (which may also be referred to as BSs, NR BSs, Node Bs, 5G NBs, APs,gNB, or some other term). As described above, a TRP may be usedinterchangeably with “cell.”

The TRPs 508 may be a distributed unit (DU). The TRPs may be connectedto one ANC (ANC 502) or more than one ANC (not illustrated). Forexample, for RAN sharing, radio as a service (RaaS), and servicespecific AND deployments, the TRP may be connected to more than one ANC.A TRP may include one or more antenna ports. The TRPs may be configuredto individually (e.g., dynamic selection) or jointly (e.g., jointtransmission) serve traffic to a UE.

The local architecture of RAN 500 may be used to illustrate fronthauldefinition. The architecture may be defined that support fronthaulingsolutions across different deployment types. For example, thearchitecture may be based at least in part on transmit networkcapabilities (e.g., bandwidth, latency, and/or jitter).

The architecture may share features and/or components with LTE.According to aspects, the next generation AN (NG-AN) 510 may supportdual connectivity with NR. The NG-AN may share a common fronthaul forLTE and NR.

The architecture may enable cooperation between and among TRPs 508. Forexample, cooperation may be preset within a TRP and/or across TRPs viathe ANC 502. According to aspects, no inter-TRP interface may beneeded/present.

According to aspects, a dynamic configuration of split logical functionsmay be present within the architecture of RAN 500. The PDCP, RLC, MACprotocol may be adaptably placed at the ANC or TRP.

According to certain aspects, a BS may include a central unit (CU)(e.g., ANC 502) and/or one or more distributed units (e.g., one or moreTRPs 508).

As indicated above, FIG. 5 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 5.

FIG. 6 illustrates an example physical architecture of a distributed RAN600, according to aspects of the present disclosure. A centralized corenetwork unit (C-CU) 602 may host core network functions. The C-CU may becentrally deployed. C-CU functionality may be offloaded (e.g., toadvanced wireless services (AWS)), in an effort to handle peak capacity.

A centralized RAN unit (C-RU) 604 may host one or more ANC functions.Optionally, the C-RU may host core network functions locally. The C-RUmay have distributed deployment. The C-RU may be closer to the networkedge.

A distributed unit (DU) 606 may host one or more TRPs. The DU may belocated at edges of the network with radio frequency (RF) functionality.

As indicated above, FIG. 6 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 6.

FIG. 7 is a diagram 700 showing an example of a DL-centric subframe orwireless communication structure. The DL-centric subframe may include acontrol portion 702. The control portion 702 may exist in the initial orbeginning portion of the DL-centric subframe. The control portion 702may include various scheduling information and/or control informationcorresponding to various portions of the DL-centric subframe. In someconfigurations, the control portion 702 may be a physical DL controlchannel (PDCCH), as indicated in FIG. 7.

The DL-centric subframe may also include a DL data portion 704. The DLdata portion 704 may sometimes be referred to as the payload of theDL-centric subframe. The DL data portion 704 may include thecommunication resources utilized to communicate DL data from thescheduling entity (e.g., UE or BS) to the subordinate entity (e.g., UE).In some configurations, the DL data portion 704 may be a physical DLshared channel (PDSCH).

The DL-centric subframe may also include an UL short burst portion 706.The UL short burst portion 706 may sometimes be referred to as an ULburst, an UL burst portion, a common UL burst, a short burst, an ULshort burst, a common UL short burst, a common UL short burst portion,and/or various other suitable terms. In some aspects, the UL short burstportion 706 may include one or more reference signals. Additionally, oralternatively, the UL short burst portion 706 may include feedbackinformation corresponding to various other portions of the DL-centricsubframe. For example, the UL short burst portion 706 may includefeedback information corresponding to the control portion 702 and/or thedata portion 704. Non-limiting examples of information that may beincluded in the UL short burst portion 706 include an ACK signal (e.g.,a PUCCH ACK, a PUSCH ACK, an immediate ACK), a NACK signal (e.g., aPUCCH NACK, a PUSCH NACK, an immediate NACK), a scheduling request (SR),a buffer status report (BSR), a HARQ indicator, a channel stateindication (CSI), a channel quality indicator (CQI), a soundingreference signal (SRS), a demodulation reference signal (DMRS), PUSCHdata, and/or various other suitable types of information. The UL shortburst portion 706 may include additional or alternative information,such as information pertaining to random access channel (RACH)procedures, scheduling requests, and various other suitable types ofinformation.

As illustrated in FIG. 7, the end of the DL data portion 704 may beseparated in time from the beginning of the UL short burst portion 706.This time separation may sometimes be referred to as a gap, a guardperiod, a guard interval, and/or various other suitable terms. Thisseparation provides time for the switch-over from DL communication(e.g., reception operation by the subordinate entity (e.g., UE)) to ULcommunication (e.g., transmission by the subordinate entity (e.g., UE)).The foregoing is merely one example of a DL-centric wirelesscommunication structure, and alternative structures having similarfeatures may exist without necessarily deviating from the aspectsdescribed herein.

As indicated above, FIG. 7 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 7.

FIG. 8 is a diagram 800 showing an example of an UL-centric subframe orwireless communication structure. The UL-centric subframe may include acontrol portion 802. The control portion 802 may exist in the initial orbeginning portion of the UL-centric subframe. The control portion 802 inFIG. 8 may be similar to the control portion 702 described above withreference to FIG. 7. In some configurations, the control portion 802 maybe a physical DL control channel (PDCCH).

The UL-centric subframe may also include an UL long burst portion 804.The UL long burst portion 804 may sometimes be referred to as thepayload of the UL-centric subframe. The UL portion may refer to thecommunication resources utilized to communicate UL data from thesubordinate entity (e.g., UE) to the scheduling entity (e.g., UE or BS).

As illustrated in FIG. 8, the end of the control portion 802 may beseparated in time from the beginning of the UL long burst portion 804.This time separation may sometimes be referred to as a gap, guardperiod, guard interval, and/or various other suitable terms. Thisseparation provides time for the switch-over from DL communication(e.g., reception operation by the scheduling entity) to UL communication(e.g., transmission by the scheduling entity).

The UL-centric subframe may also include an UL short burst portion 806.The UL short burst portion 806 in FIG. 8 may be similar to the UL shortburst portion 706 described above with reference to FIG. 7, and mayinclude any of the information described above in connection with FIG.7. The foregoing is merely one example of an UL-centric wirelesscommunication structure and alternative structures having similarfeatures may exist without necessarily deviating from the aspectsdescribed herein.

In some circumstances, two or more subordinate entities (e.g., UEs) maycommunicate with each other using sidelink signals. Real-worldapplications of such sidelink communications may include public safety,proximity services, UE-to-network relaying, vehicle-to-vehicle (V2V)communications, Internet of Everything (IoE) communications, IoTcommunications, mission-critical mesh, and/or various other suitableapplications. Generally, a sidelink signal may refer to a signalcommunicated from one subordinate entity (e.g., UE1) to anothersubordinate entity (e.g., UE2) without relaying that communicationthrough the scheduling entity (e.g., UE or BS), even though thescheduling entity may be utilized for scheduling and/or controlpurposes. In some examples, the sidelink signals may be communicatedusing a licensed spectrum (unlike wireless local area networks, whichtypically use an unlicensed spectrum).

In one example, a wireless communication structure, such as a frame, mayinclude both UL-centric subframes and DL-centric subframes. In thisexample, the ratio of UL-centric subframes to DL-centric subframes in aframe may be dynamically adjusted based at least in part on the amountof UL data and the amount of DL data that are transmitted. For example,if there is more UL data, then the ratio of UL-centric subframes toDL-centric subframes may be increased. Conversely, if there is more DLdata, then the ratio of UL-centric subframes to DL-centric subframes maybe decreased.

As indicated above, FIG. 8 is provided merely as an example. Otherexamples are possible and may differ from what was described with regardto FIG. 8.

When communicating using a wireless communication technology, such asNR, a UE may need to receive (e.g., from a base station) a referencesignal for use in obtaining one or more measurements used by the UE fora tracking operation, such as frequency tracking, time tracking, Dopplerestimation, delay spread, and/or the like.

In some cases, the base station may periodically transmit such areference signal. Use of a relatively short period between transmissionsof the reference signal to the UE may allow for improved tracking at theUE (e.g., since more frequent receptions of the TRS by the UE may allowfor more granular tracking). However, such relatively short periodsbetween the transmissions of the reference signal may result in anundesirable amount of overhead (e.g., consumption of network resources,consumption of processing resources, and/or the like) by the basestation, as compared to use of relatively longer periods betweentransmissions of the reference signal. Conversely, use of the relativelylonger periods between the transmission of the reference signal mayresult in decreased performance associated with tracking at the UE, ascompared to use of the relatively shorter periods between thetransmissions of the reference signal.

Techniques and apparatuses described herein allow a base station todetermine a signal configuration for transmitting a reference signal,associated with a tracking operation at a UE, and transmit the referencesignal based at least in part on the signal configuration. In someaspects, the signal configuration may be used to transmit a referencesignal that assists the UE with one or more measurements associated withtracking at the UE, such as a timing measurement, a frequencymeasurement, a delay spread, a Doppler estimation, a power delayprofile, and/or the like. Such a signal is referred to herein as atracking reference signal (TRS). In some aspects, the signalconfiguration, associated with the TRS, identifies a subset oflocations, of a set of locations included in a transmission window, thatis to be used to transmit the TRS.

In some aspects, such a signal configuration allows for periodictransmission of the TRS that provides for improved performance of atracking operation at the UE (e.g., as compared to use of relativelylonger periods between transmissions of the TRS), while reducingoverhead at the base station (e.g., as compared to use of shorterperiods between transmissions of the TRS).

FIG. 9 is a diagram illustrating an example 900 of determining a signalconfiguration for a transmitting a TRS to a UE, and transmitting the TRSbased at least in part on the signal configuration.

As shown in FIG. 9, and by reference number 905, a base station (e.g.,BS 110) may receive, from a UE (e.g., UE 120) signal informationassociated with the UE. In some aspects, the signal information mayinclude information based at least in part on which the base station maydetermine a signal configuration for a TRS that is to be transmitted tothe UE.

For example, the signal information may include a request for aparticular signal configuration (e.g., when the UE is capable ofidentifying a particular signal configuration that may be used by the UEto obtain one or more measurements associated with tracking at the UE).In other words, in some aspects, the UE may explicitly request aparticular signal configuration for the TRS.

As another example, the signal information may include informationassociated with a signal provided by the UE, such as information thatidentifies a signal quality, information that identifies a signalstrength, information that identifies a signal-to-noise ratio (SNR), orthe like. Here, the base station may determine the signal configurationbased at least in part on the information that identifies the signalquality, the information that identifies the signal strength, theinformation that identifies the SNR, and/or the like, as describedbelow. In other words, in some aspects, the base station may determinethe signal information based at least in part on a characteristic of aprevious communication from the UE.

Alternatively, in some aspects, the UE may not provide signalinformation to the base station. In such an aspect, the base station maydetermine the signal configuration without receiving signal informationfrom the UE (e.g., the base station may determine a default signalconfiguration, associated with the UE, that is configured on the basestation).

As further shown in FIG. 9, and by reference number 910, the basestation may determine a signal configuration for the TRS to betransmitted to the UE. In some aspects, the signal configuration mayinclude information identifying a subset of locations, of a set oflocations included in a transmission window, that is to be used totransmit the TRS to the UE.

The transmission window may include a set of locations (e.g., a windowincluding multiple slots) during which the base station may transmit aTRS. In some aspects, the transmission window may be a periodic window.For example, the base station may be configured with a transmissionwindow every 50 milliseconds (ms), every 100 ms, and/or the like (e.g.,such that the TRS may be transmitted on a periodic basis). In someaspects, a length of the transmission window may be less than or equalto approximately 10 ms, such as 2 ms, 6 ms, 10 ms and/or the like. Inother words, the length of the transmission window may be relativelyshort as compared to the period of the transmission window. For example,the length of the transmission window may be less than or equal toapproximately 10% of the period of the transmission window, less than orequal to approximately 15% of the period of the transmission window,less than or equal to approximately 20% of the period of thetransmission window, and/or the like. In some aspects, the base stationmay (e.g., before transmitting the TRS) signal window information,associated with the period and/or the length of the transmission window,to the UE. In some aspects, the base station may transmit the windowinformation using RRC signaling, a broadcast, a MAC control element, aphysical layer transmission, and/or the like.

As described above, in some aspects, the signal configuration mayinclude information identifying a subset of locations, included in thetransmission window, that is to be used to transmit the TRS to the UE.In some aspects, the subset of locations includes a number of locationsthat is less than a total number of locations included in thetransmission window. For example, the signal configuration may includeinformation that identifies a subset of slots, such as a particular slotor group of slots (e.g., a second slot; a third slot and a fourth slot;a fifth slot, a tenth slot, and a thirteenth slot, a first slot, a thirdslot, and a fifth slot, a second slot, a fourth slot, and an eighthslot, and/or the like), a pattern of slots (e.g., every third slot,every even slot, every odd slot, and/or the like), and/or the like.

In some aspects, the base station may determine the signal configurationbased at least in part on the signal information provided by the UE. Forexample, as described above, the UE may request a particular signalconfiguration. Here, the base station may determine the signalconfiguration based at least in part on the request provided by the UE.

As another example, as described above, the base station may determinethe signal configuration based at least in part on information thatidentifies a signal quality, a signal strength, a SNR, and/or the like,of a signal provided by the UE. As a particular example, if the SNR ofthe signal provided by the UE fails to satisfy a threshold, then thebase station may determine a first signal configuration includestransmissions of the TRS in a higher number of slots (e.g., as comparedto a second signal configuration that includes transmissions in a lowernumber of slots). Conversely, if the SNR of the signal provided by theUE satisfies the threshold, then the base station may determine that thesecond signal configuration is to be used for transmitting the TRS.

Additionally, or alternatively, the base station may determine thesignal configuration based at least in part on a configuration of thebase station. For example, the base station may determine a defaultsignal configuration when the UE does not receive signal informationfrom the UE.

In some aspects, the base station may transmit, to the UE, controlsignaling information that identifies the subset of locations associatedwith the signal configuration. In other words, in some aspects, the basestation may transmit, to the UE, control signaling information thatallows the UE to identify the subset of locations in which the TRS is tobe transmitted. In some aspects, the base station may transmit suchcontrol signaling information to the UE before (e.g., 1 ms before, 2 msbefore) the transmission window. In some aspects, the base station maytransmit the control signaling information using a common controlphysical downlink control channel or a physical layer signal. In someaspects, transmission of such control information conserves processingresources on the UE (e.g., since the UE may not need to attempt todetect the TRS signal in each location of the transmission window).

Alternatively, in some aspects, the base station may not transmit suchcontrol information to the UE. In such an aspect, the UE may attempt todetect (e.g., based at least in part on the window information thatidentifies the period and/or the length of the transmission window)transmissions in each location of the transmission window, and mayreceive the TRS accordingly. In other words, in some aspects, the UE mayblindly detect the TRS without a need to receive and/or decode controlsignaling information associated with the signal configuration. In someaspects, not transmitting control signaling information may reduceoverhead at the base station, and/or may conserve network resources.

Additionally, or alternatively, the base station may determine thesignal configuration based at least in part on a configurationassociated with another type of reference signal. For example, the basestation may be configured to determine the signal configuration suchthat the signal configuration matches a transmission pattern defined fora channel-state information reference signal (CSI-RS) associated withperforming beam management (e.g., where the CSI-RS is repeated over aquantity of N symbols).

As further shown in FIG. 9, and by reference number 915, the basestation may transmit the TRS in the subset of locations based at leastin part on the signal configuration. For example, as indicated in FIG.9, the base station may determine a signal configuration indicating thatthe base station is to transmit the TRS in even slots of thetransmission window, and may transmit the TRS in the even numbered slotsof the transmission window, accordingly.

As shown by reference number 920, the UE may receive the TRS transmittedin the subset of locations of the transmission window, and may obtain,based at least in part on the TRS, one or more measurements associatedwith tracking at the UE.

In some aspects, the base station may transmit another TRS in anothertransmission window based at least in part on the signal configuration.For example, after transmitting a first TRS in a subset of locations ina first transmission window, the base station may transmit a second TRSin a subset of locations in a second transmission window (e.g., a nextperiodic transmission window). In some aspects, the subset of locationsin the second transmission window may match the subset of locations inthe first transmission window (i.e., the base station may transmit thesecond TRS using the same signal configuration).

In some aspects, the base station may implement a hybrid techniqueassociated with transmitting an additional TRS in the transmissionwindow. For example, the base station may determine a signalconfiguration for transmitting a TRS in the transmission window, asdescribed above (e.g., a default signal configuration). In some aspects,the base station may determine (e.g., based at least in part on thesignal information provided by the UE) that the base station shouldtransmit an additional TRS (e.g., a TRS in addition to that associatedwith the default signal configuration) in the transmission window. Sucha determination may be made, for example, when a signal characteristic,associated with the UE, does not satisfy a threshold (e.g., when asignal quality, a signal strength, a SNR, or any combination thereof, isbelow a threshold). Here, the base station may determine an additionalsignal configuration for transmitting an additional TRS to the UE in thetransmission window. In some aspects, the additional signalconfiguration may identify an additional subset of locations (e.g., inaddition to the subset of locations identified by the default signalconfiguration) that is to be used to transmit the additional TRS. Thebase station may then transmit, based at least in part on the additionalsignal configuration, the additional TRS in the additional subset oflocations. In some aspects, the additional signal configuration caninclude an additional reference signal pattern (e.g., rather than arepetition in time). For example, if the default signal configurationdescribes a reference signal with a first frequency tone spacing (e.g.,four subcarriers), then the base station may signal an additional signalconfiguration with a second frequency tone spacing (e.g., twosubcarriers) in order to facilitate, for example, estimation of a hightiming error.

In some aspects, the base station may transmit control signalinginformation that identifies the additional subset of locations (e.g., ina manner similar to that described above). In some aspects, the basestation may transmit the control signaling information, associated withthe additional TRS (e.g., information that identifies the subset oflocations), without transmitting control signaling informationassociated with the TRS. For example, the UE may have access toinformation associated with the default signal configuration associatedwith the TRS, but may not have access to information associated with theadditional signal configuration. In such an aspect, the base station maytransmit, to the UE, control signaling information that includesinformation associated with the additional signal configuration, butdoes not include information associated with the default signalconfiguration.

As indicated above, FIG. 9 are provided as examples. Other examples arepossible and may differ from what was described with respect to FIG. 9.

FIG. 10 is a flow chart of a method 1000 of wireless communication. Themethod may be performed by base station (e.g., the base station 110 ofFIG. 1, the apparatus 1100/1102′, and/or the like).

At 1010, the base station may determine a signal configuration fortransmitting a TRS to a UE, the signal configuration identifying asubset of locations, of a set of locations included in a transmissionwindow, that is to be used to transmit the TRS, and the signalconfiguration being selected to assist the UE with one or moremeasurements. For example, the base station may determine a signalconfiguration for transmitting a TRS to a UE, where the signalconfiguration identifies a subset of locations, of a set of locationsincluded in a transmission window, that is to be used to transmit theTRS, and where the signal configuration is selected to assist the UEwith one or more measurements, as described above with regard to example900.

At 1020, the base station may transmit, based at least in part on thesignal configuration, the TRS in the subset of locations. For example,the base station may transmit, based at least in part on the signalconfiguration, the TRS in the subset of locations, as described abovewith regard to example 900.

In some aspects, the base station may transmit, to the UE, controlsignaling information that identifies the subset of locations. In someaspects, the control signaling information may be transmitted using acommon control physical downlink control channel or a physical layersignal.

In some aspects, a length of the transmission window is less than orequal to approximately 10 milliseconds.

In some aspects, the base station may determine an additional signalconfiguration for transmitting an additional TRS to the UE in thetransmission window, where, the additional signal configuration mayidentify an additional subset of locations, of the set of locationsincluded in the transmission window, that is to be used to transmit theadditional TRS; the base station may transmit control signalinginformation that identifies the additional subset of locations; and thebase station may transmit, based at least in part on the additionalsignal configuration, the additional TRS in the additional subset oflocations.

In some aspects, the base station may receive, from the UE, signalinformation for determining the signal configuration. For example, theUE may transmit, to the base station, signal information for determiningthe signal configuration associated with the TRS. Here, aftertransmission of the TRS by the base station, the UE may receive the TRSbased at least in part on transmitting the signal information to thebase station, wherein the TRS is received in the subset of locations, ofthe set of locations included in the transmission window.

In some aspects, the transmission of the TRS is a periodic transmission.

In some aspects, the one or more measurements may be associated withdetermining timing information, frequency information, a delay spread, aDoppler estimation, a power delay profile, or any combination thereof.

In some aspects, a length of time between the transmission of the TRSand another transmission of another TRS is approximately 100milliseconds.

In some aspects, the subset of locations is a first subset of locations,the transmission window is a first transmission window, and the TRS is afirst TRS. Here, the base station may transmit, based at least in parton the signal configuration, a second TRS in a second subset oflocations in a second transmission window, wherein the second subset oflocations matches the first subset of locations.

Although FIG. 10 shows example blocks of a method of wirelesscommunication, in some aspects, the method may include additionalblocks, fewer blocks, different blocks, or differently arranged blocksthan those shown in FIG. 10. Additionally, or alternatively, two or moreblocks shown in FIG. 10 may be performed in parallel.

FIG. 11 is a conceptual data flow diagram 1100 illustrating the dataflow between different modules/means/components in an example apparatus1102. The apparatus 1102 may be a base station (e.g., a base station 110of FIG. 1). In some aspects, the apparatus 1102 includes a receptionmodule 1104, a determining module 1106, and/or a transmission module1108.

The reception module 1104 may receive data 1112 from a network 1150,such as data that includes signal information associated withdetermining a signal configuration for a TRS signal to be transmitted toa UE. In some aspects, the reception module 1104 may provide data 1114to the determining module 1106. In some aspects, the data 1114 mayindicate that the determining module 1106 is to determine the signalconfiguration for transmitting the TRS to the UE. The determining module1106 may determine the signal configuration for transmitting the TRS tothe UE, as described above. In some aspects, the signal configurationincludes information identifying a subset of locations, of a set oflocations included in a transmission window, that is to be used totransmit the TRS. In some aspects, the signal configuration may beselected to assist the UE with one or more measurements.

The determining module 1106 may provide data 1116 to the transmissionmodule 1108. For example, the determining module 1106 may provide data1116, including information associated with the signal configuration, totransmission module 1108. The transmission module 1110 may transmit data1118, including the TRS, to the UE (e.g., via network 1150) in thesubset of locations based at least in part on the signal configuration,as described above.

The apparatus may include additional modules that perform each of theblocks of the algorithm in the aforementioned flow chart of FIG. 10. Assuch, each block in the aforementioned flow chart of FIG. 10 may beperformed by a module and the apparatus may include one or more of thosemodules. The modules may be one or more hardware components specificallyconfigured to carry out the stated processes/algorithm, implemented by aprocessor configured to perform the stated processes/algorithm, storedwithin a computer-readable medium for implementation by a processor, orsome combination thereof.

The number and arrangement of modules shown in FIG. 11 are provided asan example. In practice, there may be additional modules, fewer modules,different modules, or differently arranged modules than those shown inFIG. 11. Furthermore, two or more modules shown in FIG. 11 may beimplemented within a single module, or a single module shown in FIG. 11may be implemented as multiple, distributed modules. Additionally, oralternatively, a set of modules (e.g., one or more modules) shown inFIG. 11 may perform one or more functions described as being performedby another set of modules shown in FIG. 11.

FIG. 12 is a diagram 1200 illustrating an example of a hardwareimplementation for an apparatus 1102′ employing a processing system1202. The apparatus 1102′ may be a base station.

The processing system 1202 may be implemented with a bus architecture,represented generally by the bus 1204. The bus 1204 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 1202 and the overall designconstraints. The bus 1204 links together various circuits including oneor more processors and/or hardware modules, represented by the processor1206, the modules 1104, 1106, 1108, and the computer-readablemedium/memory 1208. The bus 1204 may also link various other circuitssuch as timing sources, peripherals, voltage regulators, and powermanagement circuits, which are well known in the art, and therefore,will not be described any further.

The processing system 1202 may be coupled to a transceiver 1210. Thetransceiver 1210 is coupled to one or more antennas 1212. Thetransceiver 1210 provides a means for communicating with various otherapparatus over a transmission medium. The transceiver 1210 receives asignal from the one or more antennas 1212, extracts information from thereceived signal, and provides the extracted information to theprocessing system 1202, specifically the reception module 1104. Inaddition, the transceiver 1210 receives information from the processingsystem 1202, specifically the transmission module 1110, and based atleast in part on the received information, generates a signal to beapplied to the one or more antennas 1212. The processing system 1202includes a processor 1206 coupled to a computer-readable medium/memory1208. The processor 1206 is responsible for general processing,including the execution of software stored on the computer-readablemedium/memory 1208. The software, when executed by the processor 1206,causes the processing system 1202 to perform the various functionsdescribed supra for any particular apparatus. The computer-readablemedium/memory 1208 may also be used for storing data that is manipulatedby the processor 1206 when executing software. The processing systemfurther includes at least one of the modules 1104, 1106, and 1108. Themodules may be software modules running in the processor 1206,resident/stored in the computer-readable medium/memory 1208, one or morehardware modules coupled to the processor 1206, or some combinationthereof. The processing system 1202 may be a component of the basestation 110 and may include the memory 242 and/or at least one of the TXMIMO processor 230, the RX processor 238, and/or thecontroller/processor 240.

In some aspects, the apparatus 1102/102′ for wireless communicationincludes means for determining a signal configuration for transmitting aTRS to a UE, where the signal configuration may identify a subset oflocations, of a set of locations included in a transmission window, thatis to be used to transmit the TRS, and the signal configuration isselected to assist the UE with one or more measurements; and means fortransmitting, based at least in part on the signal configuration, theTRS in the subset of locations.

In some aspects, the apparatus 1102/102′ for wireless communicationincludes means for transmitting control signaling information thatidentifies the subset of locations. In some aspects, the controlsignaling information is transmitted using a common control physicaldownlink control channel or a physical layer signal.

In some aspects, a length of the transmission window is less than orequal to approximately 10 milliseconds.

In some aspects, the apparatus 1102/102′ for wireless communicationincludes means for determining an additional signal configuration fortransmitting an additional TRS to the UE in the transmission window,where the additional signal configuration may identify an additionalsubset of locations, of the set of locations included in thetransmission window, that is to be used to transmit the additional TRS;means for transmitting control signaling information that identifies theadditional subset of locations; and means for transmitting, based atleast in part on the additional signal configuration, the additional TRSin the additional subset of locations.

In some aspects, the apparatus 1102/102′ for wireless communicationincludes means for receiving, from the UE, signal information fordetermining the signal configuration.

In some aspects, the transmission of the TRS is a periodic transmission.

In some aspects, the one or more measurements are associated withdetermining timing information, frequency information, a delay spread, aDoppler estimation, a power delay profile, or any combination thereof.

In some aspects, a length of time between the transmitting of the TRSand another transmission of another TRS is approximately 100milliseconds.

In some aspects, the subset of locations is a first subset of locations,the transmission window is a first transmission window, and the TRS is afirst TRS; and the apparatus 1102/102′ for wireless communicationincludes means for transmitting, based at least in part on the signalconfiguration, a second TRS in a second subset of locations in a secondtransmission window, where the second subset of locations matches thefirst subset of locations.

The aforementioned means may be one or more of the aforementionedmodules of the apparatus 1102 and/or the processing system 1202 of theapparatus 1102′ configured to perform the functions recited by theaforementioned means. As described supra, the processing system 1202 mayinclude the TX MIMO Processor 230, the RX Processor 238, and/or thecontroller/processor 240. As such, in one configuration, theaforementioned means may be the TX Processor 230, the RX Processor 238,and/or the controller/processor 240 configured to perform the functionsrecited by the aforementioned means.

FIG. 12 is provided as an example. Other examples are possible and maydiffer from what was described in connection with FIG. 12.

It is understood that the specific order or hierarchy of blocks in theprocesses/flow charts disclosed is an illustration of exampleapproaches. Based upon design preferences, it is understood that thespecific order or hierarchy of blocks in the processes/flow charts maybe rearranged. Further, some blocks may be combined or omitted. Theaccompanying method claims present elements of the various blocks in asample order, and are not meant to be limited to the specific order orhierarchy presented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” The word “exemplary” is used hereinto mean “serving as an example, instance, or illustration.” Any aspectdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects. Unless specifically statedotherwise, the term “some” refers to one or more. Combinations such as“at least one of A, B, or C,” “at least one of A, B, and C,” and “A, B,C, or any combination thereof” include any combination of A, B, and/orC, and may include multiples of A, multiples of B, or multiples of C.Specifically, combinations such as “at least one of A, B, or C,” “atleast one of A, B, and C,” and “A, B, C, or any combination thereof” maybe A only, B only, C only, A and B, A and C, B and C, or A and B and C,where any such combinations may contain one or more member or members ofA, B, or C. All structural and functional equivalents to the elements ofthe various aspects described throughout this disclosure that are knownor later come to be known to those of ordinary skill in the art areexpressly incorporated herein by reference and are intended to beencompassed by the claims. Moreover, nothing disclosed herein isintended to be dedicated to the public regardless of whether suchdisclosure is explicitly recited in the claims. No claim element is tobe construed as a means plus function unless the element is expresslyrecited using the phrase “means for.”

What is claimed is:
 1. A method of wireless communication, comprising:determining, by a base station, a signal configuration for transmittinga tracking reference signal (TRS) to a user equipment (UE), the signalconfiguration identifying a subset of locations, of a set of locationsincluded in a transmission window, that is to be used to transmit theTRS, and the signal configuration selected to assist the UE with one ormore measurements; transmitting, by the base station and based at leastin part on the signal configuration, the TRS in the subset of locations;determining an additional signal configuration for transmitting anadditional TRS to the UE; and transmitting, based at least in part onthe additional signal configuration, the additional TRS.
 2. The methodof claim 1, further comprising transmitting, to the UE, controlsignaling information that identifies the subset of locations.
 3. Themethod of claim 2, wherein the control signaling information istransmitted using a common control physical downlink control channel ora physical layer signal.
 4. The method of claim 1, wherein a length ofthe transmission window is less than or equal to approximately 10milliseconds.
 5. The method of claim 1, wherein the additional signalconfiguration identifies an additional subset of locations, of the setof locations included in the transmission window, that is to be used totransmit the additional TRS, wherein the method further comprises:transmitting control signaling information that identifies theadditional subset of locations, and wherein the additional TRS istransmitted in the additional subset of locations.
 6. The method ofclaim 1, further comprising receiving, from the UE, signal informationfor determining the signal configuration.
 7. The method of claim 1,wherein the transmission of the TRS is a periodic transmission.
 8. Themethod of claim 1, wherein the one or more measurements are associatedwith determining timing information, frequency information, a delayspread, a Doppler estimation, a power delay profile, or any combinationthereof.
 9. The method of claim 1, wherein a length of time between thetransmitting of the TRS and the transmitting of the additional TRS isapproximately 100 milliseconds.
 10. The method of claim 1, wherein thesubset of locations is a first subset of locations, the transmissionwindow is a first transmission window, and the TRS is a first TRS,wherein the additional TRS is a second TRS that is transmitted in asecond subset of locations in a second transmission window, and whereinthe second subset of locations matches the first subset of locations.11. An apparatus, comprising: a memory; and at least one processorcoupled to the memory, the at least one processor being configured to:determine a first signal configuration for transmitting a first trackingreference signal (TRS) to a user equipment (UE), the first signalconfiguration identifying a first subset of locations, of a set oflocations included in a first transmission window, that is to be used totransmit the first TRS, and the first signal configuration selected toassist the UE with one or more measurements; transmit, based at least inpart on the first signal configuration, the first TRS in the firstsubset of locations; and transmit, based at least in part on the firstsignal configuration or a second signal configuration, a second TRS in asecond subset of locations in a second transmission window.
 12. Theapparatus of claim 11, wherein the at least one processor is furtherconfigured to transmit, to the UE, control signaling information thatidentifies the first subset of locations.
 13. The apparatus of claim 11,wherein a length of the first transmission window is less than or equalto approximately 10 milliseconds.
 14. The apparatus of claim 11, whereinthe at least one processor is further configured to: determine thesecond signal configuration for transmitting the second TRS to the UE,the second signal configuration identifying the second subset oflocations; and transmit control signaling information that identifiesthe second subset of locations.
 15. The apparatus of claim 11, whereinthe at least one processor is further configured to receive, from theUE, signal information for determining the first signal configuration.16. The apparatus of claim 11, wherein the transmission of the first TRSis a periodic transmission.
 17. The apparatus of claim 11, wherein theone or more measurements are associated with determining timinginformation, frequency information, a delay spread, a Dopplerestimation, a power delay profile, or any combination thereof.
 18. Theapparatus of claim 11, wherein a length of time between the transmittingof the TRS and the transmitting of the second TRS is approximately 100milliseconds.
 19. The apparatus of claim 11, wherein the second subsetof locations matches the first subset of locations.
 20. An apparatus,comprising: means for determining a signal configuration fortransmitting a tracking reference signal (TRS) to a user equipment (UE),the signal configuration identifying a subset of locations, of a set oflocations included in a transmission window, that is to be used totransmit the TRS, and the signal configuration selected to assist the UEwith one or more measurements; means for transmitting, based at least inpart on the signal configuration, the TRS in the subset of locations;means for determining an additional signal configuration fortransmitting an additional TRS to the UE; and means for transmitting,based at least in part on the additional signal configuration, theadditional TRS.
 21. The apparatus of claim 20, further comprising meansfor transmitting, to the UE, control signaling information thatidentifies the subset of locations.
 22. The apparatus of claim 20,wherein a length of the transmission window is less than or equal toapproximately 10 milliseconds.
 23. The apparatus of claim 20, whereinthe additional signal configuration identifies an additional subset oflocations, of the set of locations included in the transmission window,that is to be used to transmit the additional TRS, wherein the apparatusfurther comprises: means for transmitting control signaling informationthat identifies the additional subset of locations, and wherein theadditional TRS is transmitted in the additional subset of locations. 24.The apparatus of claim 20, further comprising means for receiving, fromthe UE, signal information for determining the signal configuration. 25.The apparatus of claim 20, wherein the transmission of the TRS is aperiodic transmission.
 26. The apparatus of claim 20, wherein the one ormore measurements are associated with determining timing information,frequency information, a delay spread, a Doppler estimation, a powerdelay profile, or any combination thereof.
 27. The apparatus of claim20, wherein a length of time between the transmitting of the TRS and thetransmitting of the additional TRS is approximately 100 milliseconds.28. The apparatus of claim 20, wherein the subset of locations is afirst subset of locations, the transmission window is a firsttransmission window, and the TRS is a first TRS, wherein the additionalTRS is a second TRS that is transmitted in a second subset of locationsin a second transmission window, and wherein the second subset oflocations matches the first subset of locations.
 29. A non-transitorycomputer-readable medium storing computer executable code that, whenexecuted by at least one processor, cause the at least one processor to:determine a signal configuration for transmitting a tracking referencesignal (TRS) to a user equipment (UE), the signal configurationidentifying a subset of locations, of a set of locations included in atransmission window, that is to be used to transmit the TRS, and thesignal configuration selected to assist the UE with one or moremeasurements; transmit, based at least in part on the signalconfiguration, the TRS in the subset of locations; transmit controlsignaling information that identifies an additional subset of locations;and transmit an additional TRS in the additional subset of locations.30. The non-transitory computer-readable medium of claim 29, wherein thecontrol signaling information is transmitted to the UE.